1. Field of the Invention
The present invention relates to a user input device and, more particularly, to a user input device for a computer system.
2. Description of the Related Art
User input devices for computer systems can take many forms. Two forms of user input devices of interest are touch screens and pen-based screens. Touch screens provide a user's input by way of a user touching a display screen with one's finger. Pen-based screens provide a user's input by way of a user touching a display screen with a stylus or pen.
One conventional approach to providing touch or pen-based screens is to overlay a resistive or capacitive film over the display screen. One problem of the conventional film approach is that the films are easily damaged. Another problem with the conventional film approach is that the cost of this approach tends to be too expensive for standard size or larger display screens because it scales quadratically with perimeter. Another problem of the conventional film approach is that the largely translucent film is laid over the display screen. The film thus causes the display screen to appear dimmed. To compensate, the display screen could offer a greater intensity of light output but such is not always sufficiently available. For example, in the case of portable computers, additional light intensity is usually not available and, if it were, it would lead to additional power consumption that strains the battery of the portable computer.
Another approach to providing touch or pen-based screens is to use banks of infrared Light Emitting Diodes (LEDs) to provide light and a corresponding bank of phototransistors to detect the light. A major problem of the conventional light-based approach is that it requires a large number of components. The components are also too large for use on portable computers. Another problem with the conventional light-based approach is that it is unable to provide the high resolution needed for pen-based screens. Additionally, the conventional light-based approaches are expensive given the large number of components required.
Another approach to providing touch or pen-based screens is to use a bundle of fiber optic cables, a liquid crystal display (LCD) as a controllable mask, and a multiplexing scheme. Such an approach is described in U.S. Pat. No. 5,196,836. Here, although only a single light emitter is used, the spreading of the light output from the fiber optic cables is severe such that controllable LCD masks are needed to sequentially isolate light output from only one fiber optic cable at a time. The reception of the light from an isolated fiber optic cable is also isolated on the reception side. Given this arrangement, the system has to scan through each of the fiber optic cables using the multiplexing scheme which makes the approach very slow. Furthermore, this approach cannot yield high resolution needed for pen-based screens and is also rather expensive to fabricate.
Thus, there is a need for improved user input devices that can provide high resolution at moderate cost.